This invention relates to production of dry water-dispersible compositions containing microencapsulated pesticides.
Microencapsulation is one of the techniques or methods utilized in producing pesticidal compositions, and is particularly useful in producing compositions containing low-melting solid pesticides. For the most part, microencapsulation of pesticides is utilized when a slow or controlled release of the pesticide is desired. This is accomplished by encapsulating particles or droplets of a material containing a pesticide within a polymeric shell through which the pesticide migrates at a controlled rate. The rate of release of the pesticide is determined by both the nature of the pesticide and by the type, structure and properties of the capsule shell. The nature of the shell, in turn, can be predetermined or constructed, as is known in the art, by selection of the type and quantity of polymer and the conditions under which the shell wall is formed.
Microencapsulated formulations or compositions have a number of additional advantages relating to safety and toxicity. Since the pesticide is contained within a polymeric wall, there is in general less dusting and much lower toxicity associated with the production, handling and application of pesticides so formulated, as well as lower animal toxicity.
It is also possible to produce microencapsulated formulations of pesticides in which controlled release is not the objective. Such compositions contain the pesticide in microcapsules which are generally on the smaller side, and tend to have relatively thin walls. Microencapsulated pesticides of this type would be intended for certain foliar applications, in situations in which a relatively quick release of the entire contents of the microcapsules is desired. However, even though controlled release may not be an objective, it is nevertheless desirable to take advantage of the lessened toxicity and dust formation of microencapsulated pesticides as compared to non-microencapsulated forms.
Microencapsulated pesticides, whether of the controlled release or the quick release variety, are usually sold in the form of aqueous suspensions of the microcapsules. Such suspensions naturally result from the process for the production of microcapsules which in general involves the formation of a dispersion or emulsion of a relatively non-water soluble liquid (xe2x80x9coilxe2x80x9d) in an aqueous medium. The oil phase contains a pesticide to be encapsulated as well as one or more monomers which will form the polymeric microcapsule wall. The microencapsulated products are produced by forming the oil/water dispersion, followed by heating and other means to produce polymerization, resulting in polymeric microcapsules containing the non-water soluble liquid material, suspended in the aqueous phase.
In general, it would be further advantageous to provide such microencapsulated compositions in dry form, rather than as aqueous suspensions. Dry formulations may be prepared with relatively high loading of the pesticide, are easier to remove from containers, produce less contamination in the environment, may be stored for long periods of time, and their storage and transportation does not require the simultaneous storage and transport of large volumes of water. In addition, since pesticidal microcapsules are typically applied by dilution of the microencapsulated formulation with water in a spray tank to form a sprayable emulsion, it would be convenient to provide a solid formulation of microencapsulated pesticides which is water dispersible, i.e., can easily be mixed with water to produce such a sprayable material.
In one aspect, this invention comprises a process for the production of a water-dispersible composition containing a microencapsulated pesticide, said process comprising (a) preparing an aqueous suspension comprising microcapsules containing at least one water-insoluble pesticide enclosed within a polymeric shell suspended in an aqueous medium containing a water-soluble polymer; and (b) spray-drying the aqueous suspension of step (a) to produce a water-dispersible composition comprising said microcapsules in a matrix comprising the water-soluble polymer, wherein the water-soluble polymer comprises from about 4 to about 15 weight percent of the water-dispersible composition.
A second aspect of the invention comprises the products thus prepared, which comprise microcapsules containing at least one water-insoluble pesticide within a polymeric shell, the microcapsules being contained within a matrix comprising a water-soluble polymer, the water-soluble polymer comprising from about 4 to about 15 weight percent of the water-dispersible composition.